Cathode-ray tube deflecting circuit



N O S m T A. w

CATHODE-RAY TUBE DEFLECTING CICUIT INVENTOR VVz'lliam LTQlSon Sept. 19,1939. w. A. ToLsoN 2,173,239

CATHODE-HAY TUBE DEFLECTING CIRCUIT Filed July 27, 1934 '2 Sheets-Sheet2 Zit-V58 .213@ n-/ l 7j 'la 71 HV Patented Sept. i9, i939 UNITED STATESPATENT Aomi-ice mesne assignments, to Radi York,y

-America., New

laware o Corporation of N. Y., a. corporation of pplication July 27,1934, Serial No. 737,163

11 Claims.

'I'he present invention relates to cathode-ray tube deflecting circuitsand particularly to circuits for applying a deflecting voltage toelectrostatic deecting plates in a television receiver tube.

In cathode-ray tubes in which the electron beam is to be deected atahigh frequency and, especially, in which the electron beam must be venvelope of the cathode-ray tube. Even with this construction, thedeflecting voltage must be rather high.

With the deflecting plates inside a cathode-ray tube of the type thisdiiiculty apparently being a result of the de:

fleeting plates '30 it is impossible to design a transformer which doesnot have a resonant point. Consequently, the transformer introducedtransient voltages into 35 non-uniform speed.

It is, accordingly, an object of my invention to provide an improvedelectrostatic deilecting circuit for a cathode-ray tube.

More specifically, it is an object of my inven- 40 tion to provide anelectrostatic deflecting circuit for a cathode-ray tube of the typeutilizing electrostatic focusing which does not involve theabove-mentioned disadvantages.

In a preferred embodiment of my invention, my 45 improved deectingcircuit is utilized for impressing a voltage having a saw-tooth waveshape upon the deflecting plates in a cathode-ray tube of theabove-mentioned type. An auto-transformer is employed for increasing thesaw-tooth voltage 50 to the desired value, the auto-transformer being sodesigned that it does not resonate at any frequency which is a necessarycomponent of the saw-tooth voltage wave. Transient voltages areprevented from appearing on the deecting plates 55 by means of a filterpreceding the auto-,trans- (Cl. P18-7.7)

former which attenuates all frequency components having a frequency ashigh as the resonant point of the transformer.

In order to prevent defocusing of the electron beam, the voltage acrossthe transformer is applied to the deflecting plates through a specialpotentiometer circuit.

Other objects, features, and advantages of my invention will appear fromthe following description taken in connection with the accompanyingdrawings in which,

Figure 1 is a circuit diagram of a television receiver embodying myinvention;

Figure 2 is a group of curves which are referred to in explaining theoperation of a portion of the circuit shown in Figure 1;

Figure 3 is a curve showing the frequency response characteristic of anamplifier in the horizontal defiectingcircuit shown in Figure 1;

Figure 4,is a diagram which is referred to in explaining the action ofthe auto-transformer shown in Figure 1; and

Figures 5 and 6 are diagrams which are referred to in explaining theoperation of the horizontal deilecting circuit.

Referring to Figure 1, my invention is shown applied to a televisionreceiver which includes a cathode-ray tube I comprising an evacuatedenvelope 3 having an electron gun therein. The electron gun consists ofan indirectly heated cathode 5, a control grid l, a screen grid 9, and afirst anode II. 'I'he electron beam is focused the desired amount by theelectron gun and by a second anode I5 to obtain the desired small spoton the fluorescent screen I3 at the end of the envelope 3. The anode I5may be in the form of a metallic coating on the inner surface of theenvelope. Will be seen that the second anode I5 functions as anelectrostatic focusing electrode as Well as means for accelerating theelectrons to the necessary velocity for obtaining a bright spot on theuorescent screen I3.

Electrostatic deecting plates Il are located in'- vside the envelope 3for dei'lecting the electron beam in a horizontal direction. Thevertical deflection of the beam is preferably obtained by means ofdeecting coils I9. The cathode-ray tube described above is of the typedescribed more in detail in the article by Taylor, Headrick, and Orthappearing inElectronics for December, 1933. In that article the mannerin which the electron beam is focused is described. It may be noted thatin some instances it is preferred to omit the screen or acceleratinggrid 9.

The receiving apparatus for applying picture impulses-as ing application,Seriali No f 1934; thej transmitter iw v r signals dei; :withtneteievisiaa new is ef the@ einig reduit )il eig in i This separatingcircuit; is

zontall de v oscil-i lator or driver tube 39, an impulse tube Albanamplifier tube 43, and a power output tube 45. The blocking oscillatortube 39 may bev of the screen grid type including a cathode 41, a.control grid 49, a screen grid 5|, a suppressor grid 53 and an anode 55.The control grid 49 is connected through a. grid leak resistor 51 andthrough a bias battery l.39 to ground and through ground to the cathode41. The grid circuit of the oscillator 33 also includes a grid condenser6|, the secondary 63 of a transformer 65 and a coupling resistor E'l;the grid condenser, the secondary and the resistor being connected inseries.

The anode 55 is connected through the primary 69 of the transformer 155to a suitable source of positive potential. The screen grid 5I issupplied with positive potential in accordance with ordinary practicewhile the suppressor grid 53 is connected to the cathode 41.

The bias voltage applied to the control grid 49 by the biasing battery59 is such that the oscillator will not oscillate unless a voltageimpulse is applied to the circ 't from an external source and, when suchan impulse is applied to the circuit, it'will oscillate through only onecycle and then stop.v In the usual sense, therefore, the device is notan oscillator since it will not oscillate continuously of its ownaccord.

The operation of the blocking oscillator tube 39 as a driver tube willbe understood by referring to Fig. 2, which indicates wave shapeand'phase relation but not relative magnitude. In this ngure, thehorizontal synchronizing impulse which appears across the couplingresistor 61 is represented by the curve 1|, while the resulting volt-`pling circuit performs ,sl harglfillfolhzii i? tube.

The resulting awetic amplified by the amplifier tube 43 and impress uponthe input circuit of the power tube through a coupling circuit whichincludes an inductance coil 8| and a blocking condenser 83.

The inductance coil 8| is of such value that it resonates with thegrid-cathode capacity of the power tube 45 at the high frequency. end ofthe band of frequencies to be amplified. In some cases, additionalcapacity should be connected between the grid of the tube 45 and ground,as indicated at 85, in order to obtain a resonant point at the desiredfrequency. The tuned coutwo functions, one being to increase theresponse of the amplier'43-45 at the higher frequencies and the otherbeing to cut off the highest frequency components of the same tooth wavefor a purpose which Will be described later.

The effect of the inductance coil 8| resonating with the capacity of theinput circuit of the tube 45 is shown by the curve 81 in Fig. 3. It willbe seen that at the high frequency end of the curve 81 the gain of theamplifier is maintained at a high level and that beyond the point ofresonance of the coil 8| and the tube capacity (indicated at 89) thegain drops off very rapidly.

After being amplified in the power tube 45, the saw-tooth voltage W'aveis impressed through a coupling condenser 9| upon the primary of anauto-transformer 93. In order to prevent defocusing of the electron beamin the cathode-ray tube l during deflection, as explained hereinafter,the midpoint of the transformer Winding 93 should be connected to groundas shown, this ieinem:szatieecnaitien hef;

l leakage inductances midpoint being one end of the primary section ofthe autoetransformer.

The saw-tooth voltage wave appears at a much higher voltage across theterminals of the transformer secondary and is impressed upon thedeetisnlg plates i through blocking condensers an It has been found thatde-focusing of the cathode beam during deection is prevented if thevoltage on the deflecting plates ii is varied about the second anodepotential. In order to obtain this result, a high resistancepotentiometer 99 is connected across the deecting plates i'l'and thesecond anode I5 is connected through a conductor |0| to the midpoint ofthe potentiometer 99. It will be noted that the potentiometer 99 is alsoconnected across the transformer secondary through the blockingcondensers 95 and 91. By means of this circuit, upon the ap. plicationof a deecting voltage'to the electrostatic deiiecting plates i1, whenone plate is made positive a certain amount, the other plate is madenegative an equal amount and the potential at a point half Way betweenthe deecting plates remains unchanged. It is believed that because ofthis fact the electrostatic focusing eld is not distorted, with theresult that there is no de-focusing during deflection of the electronbeam.

In employing a transformer for obtaining the desired high voltage on thedeecting plates, difficulty was encountered because of the leakageinductance of the transformer resonating with its distributed capacityat a certain high frequency, with the result that the resonance of thetransformer introduced undesirable tran` sients into the deiiectingcircuit. The effect of these transients is shown in Figure 6. It will benoted that at the beginning of each saw-tooth wave there are transientsor irregularities in the wave shape indicated at |03 Whereas a voltagehaving the wave shape shown sired.

The reason for the occurrence of the transients on the deflecting plateswill be better understood by referring to Figure 4 where the equivaientdiagram for the auto-transformer 93 is shown. The mutual inductance ofthe transformer is indicated at |05 while the primary and secondaryleakage inductances are indicated at |67 and |69, respectively. Theoutput circuit of the power tube is represented by the alternatingcurrent generator IH and resistor H3. The distributed capacity of thetransformer winding is represented by the condenser H5 while thedei'lecting plates il of the cathode ray tube are shown connected acrossthe output terminals of the transformer. It will be seen that thedistributed capacity i'i is in series with the two |07 and |09 whereby aseries resonance circuit is formed which is resonant at a highfrequency.

In accordance with one of the features of my invention, the transients|03 are eliminated by reducing the leakage inductance of the transformer93 to a minimum whereby the resonant frequency is made higher than anyfrequency component which must be transmitted to obtain a satisfactorysaw-tooth voltage wave and, since the resonant frequency is still Withinthe range of frequencies included in the saw-tooth wave being generated,shock excitation of the transformer resonant circuit is prevented bycutting off the high frequency components of the sawtooth defiectingwave at a frequency below the in Figure 5 is deeluded in the circuit inseries resonant point of the transformer. This is ac complished, asshown in Figure 3, by means of the above-described tuned couplingcircuit ill-83. In Figure 3, the leakage resonant point of thetransformer 93 is indicated by the dotted line H1. It will b e seen thatby resonating the inductance coil 8| with the tube capacity, theamplifier is in eiect given a sharp cut-olf at a frequency below theresonant point of the transformer 93.

It has been found that, in order to obtain satisfactory results, thetransformer 93 must not be resonant at any point Withinthe range offrequencies which are impressed thereon. For this reason the transformermust be so designed that at the low end of the range of frequencies tobe transmitted, the mutual inductance |05 of the transformer will notresonate with the distributed capacity H 5 at too highv a frequency.Therefore the transformer is so designed that its resonant point at thelow frequency end is considerably below the fundamental frequency of thehorizontal saw-tooth Waves. For example, if the horizontal deflectingfrequency is 10,000 cycles per second the transformer may be so designedthat its low frequency resonant point is at '7,000 cycles per second.

Vertical deiiection of the electron beam preferably is obtained by meansof the deflecting coils I9 in View of the comparatively low frequency atwhich the vertical deflection occurs. The vertical deflecting circuitmay include the blocking oscillator 31 comprising a vacuum tube l I9which is biased by means of a biasing battery |2| beyond the cut-offpoint the same as the oscillator tube 39 in the horizontal deflectingcircuit. The oscillator includes grid condenser |23, a grid leakresistor |25, and a feed-back transformer |21, all of which performedthe functions described in connection with the horizontal blockingoscillator.

The vertical synchronizing impulses are impressed upon the grid circuitof the tube H9 through a coupling resistor |29 which is inwiththe-secondary of the transformer |27. Preferably, a condenser |3| isprovided for by-passing any horizontal synchronizing impulse componentwhich may not be nltered out by the'inductance coil 35.

rThe positive voltage impulses which appear in the grid circuit of thedriver tube i I9 in response to the reception of a verticalsynchronizing impulse are impressed through a coupling condenser |33-upon an impulse tube |35. The output circuit of the impulse tube |35includes a condenser |37 having a variable resistor |39 connected inseries therewith for supplying a voltage impulse wave containing asaw-tooth component. This voltage wave appears across the input circuitof a vpower tube Mii and is impressed across the deecting coils I9 toproduce a saw-tooth wave of current therethrough. The

resistor |53, to which one terminal of the defleeting coils i9 isconnected, is provided for the purpose of adjusting the direct currentcomponent through the deflecting coils to center the electron beam onthe fluorescent screen i3.

Referring now to the voltage supplies for the deecting circuits and forthe cathode-ray tube I, all the voltages for the vacuum tubes aresupplied from a low voltage supply M5 across which a voltage divider miis connected. All the plates of the vacuum tubes are connected to thepositive terminal of the voltage divider |41, The screen grids of thescreen grid tubes are connected to a point of lower potentialon thevoltage divider |41 as indicated. The screen grid 8 of the cathode-raytube is connected to a point of still lower potential on the voltagedivider |41.

The cathode 5 of the cathode-ray tube I is connected to ground and to apoint on the voltage divider |41 near its negative end, while thecontrol electrode 1 of the cathode-ray tube is connected tothe negativeend of the voltage divider |41 through a resistor |49 for maintaining itat the proper negative potential with respect to the cathode 5.

The higher voltages for the anodes and I5 of the cathode-ray tube areprovided by a higher voltage supply |5| having a voltage dividerv |53connected thereacross. The negative end of the voltage divider |53 isconnected through ground to the cathode 5 of the cathode-ray tube. Thesecond anode l5 is connected to the positive end of the voltage dividerlwhile the first anode is connected to a point of lower potential on thesaid voltage divider.

In either embodiment of my invention, the impulse tubes 4| and |35 arepreferably biased be biased inserting a biasing battery (not shown) inthe grid circuit. In the particular circuit illustrated, which is thepreferred one, the tubes il and |35 are biased close to cut-olf by meansof the ow of grid current in the coupling condenser-grid resistorcombination.

Referring to the tube 4| as an example, a positive voltage impulse fromthe blocking oscillator 33 causes a iiow of grid current to charge thecondenser 15, Between positive voltage impulses, the condenserdischarges through the grid resistor 16 to maintain the grid of the tube4| negatively biased. If the blocking oscillator is replaced by anamplifier (two resistance coupled vacuum tubes, for example) the biasingcircuit shown is especially desirable as the bias on the impulse tube 3|increases with increase in signal strength whereby an automatic volumeaction is obtained.

The features of using a blocking oscillator 33 as a driver tube and ofdriving a deecing circuit directly and re-shaping a. synchronizingimpulse into a saw-tooth voltage or current wave are described andclaimed in my above-mentioned co-pending application Serial No. 732,415,which is assignedv to the same assignee as this application.

It will be seen from the foregoing description that I have provided adeecting circuit in which a comparatively small power or amplifier tubesupplies sufficient voltage to the electrostatic deflecting plates of acathode ray tube to deiiect the electron beam the desired amount withoutintroducing transients during deflection. It will also be seen that Ihave provided a means for applying a deflecting voltage to internaldeflecting plates in a cathode-ray tube without causing the electronbeam to be de-focused.

It will be understood that various modifications may be made in myinvention without departing from the spirit and scope thereof and Idesire, therefore, that only such limitations shall be placed thereon asare necessitated by the prior art and are set forth in the appendedclaims.

I claim as my invention: A

l. In combination, a cathode-ray tube comprising an evacuated envelopehaving means therein for producing a beam of electrons, a pair ofdeflecting plates therein for Adeflecting said beam, atransformer havinga primary and a secondary, said transformer having leakage inductanceand distributed capacity which resonate at a high resonant frequency toproduce undesired effects, means for coupling said secondary across saiddeflecting plates, an amplifier having an output circuit and designed topass a wide band of frequencies, said output circuit being connected tosaid primary, and means for preventing energy having a frequency as highas said resonant frequency from being impressed upon said primary.

2. Apparatus according to claim 1 characterized in that said amplifierincludes an electric discharge tube comprising input electrodes havingcapacity effectively in shunt thereto, and further characterized in thatsaid last means includes an inductance coil which is connected in serieswith said capacity and which has a value such that it resonates withsaid capacity at a frequency below the said resonant frequency of saidtransformer.

3. In a picture receiver, a cathode-ray tube comprlsing an evacuatedenvelope having means therein for producing a beam of electrons, a pairof deflecting plates therein for deflecting said beam, means forgenerating electrical deflecting impulses having a saw-tooth wave shape,means including a transformer for impressing said deecting impulses uponsaid deflecting plates, said transformer being resonant at a certainhigh frequency, and means for preventing components of said impulseshaving a frequency as high as said certain frequency from beingimpressed upon said transformer.

4. In combination, a cathode-ray tube comprising an evacuated envelopehaving means therein for producing a beam of electrons, electrostaticmeans for focusing said beam, said electrostatic means including asecond anode, a pair of deecting plates in said envelope for deflectingsaid beam, a source of deiiecting voltage for said plates, a transformerhaving a primary and a secondary, said primary being connected to saidsource, and an impedance unit having one end connected to one end ofsaid secondary through a condenser and having its other end connected tothe other end of said secondary through another condenser, saiddeiiecting plates being connected across said impedance unit, and saidsecond anode vbeing connected to a point on said impedance unit whichisa mid-point with respect to the points thereon to which saiddeflecting plates are connected. l

5. In combination, a cathode-ray tube comprising an evacuated envelopehaving means therein for producing .a beam of electrons, an electrodepositioned to focus said beam electrostatically, a pair of electrostaticdeflecting plates in said envelope for deflecting said beam, a source ofdeiiecting voltage for said plates, a transformer having a primary and asecondary, said primary being connected to said source, and a resistorconnected across said secondary through blocking condensers, saiddeflecting plates being connected across said resistor, and saidfocusing electrode being connected to a point on said resistor which isthe mid-point with respect to the points thereon to which saiddefleeting plates are connected.

6. In combination, a cathode-ray tube comprising an evacuated envelopehaving an electron gun therein for producing a beam of electrons, saidgun including a cathode, an electrostatic focusing electrode positionedto focus said beam, -a pair of electrostatic deecting plates in saidenvelope for deecting said beam, a source of deflecting voltage for saidplates, a transformer having a primary and a secondary, said primarybeing connected to said source and said secondsaid source and to said y2,173,289 f v 5 ary having its mid-point connected to said ponents allof which lie between said low i'recathode', a resistor connected acrosssaid secondquency resonant point and Isaid high frequency ary throughblocking condensers. said deilectresonant point, and means' forimpressing said ing plates being connected across said resistor.lsaw-tooth wave across said primary.

said focusing electrode being connected to the mid-point of s'aidresistor, .taining said focusing electrode at a positive potential withrespect to said cathode.

7. In combination, a cathode-ray tube comprising an evacuated envelopehaving an electron 'gun therein for producing a beam of electrons.

a source of deecting voltage for said plates, a single windingtransformer, the mid-point of said winding being connected to oneterminal of cathode whereby Iit is maintained at the same alternatingcurrent potential as said cathode and another point on said windingbeing connected to the other terminal oi' said source, a resistorconnected across said wind. ing through blocking condensers, saiddeecting plates being connected across said resistor, said focusingelectrode being connected to the midpoint of said resistor. and meansfor maintaining said focusing electrode at a positive potential withrespect to said cathode.

8. In combination, a cathode ray tube comprising an evacuated envelopehaving means therein for producing a beam of electrons, a pair ofdeiiecting platestherein for deilecting said beam, a transformer havinga primary and a secondary, said transformer having a low fre.- quencyresonant point and a high frequency resonant point and having noresonant point therebetween, means for coupling said deecting platesacross said secondary, means for producing a saw-tooth wave havingfrequency comand means for main- A cathode ray device comprising meansfor producing aI moving beam oi electrons, an anode means for connectingsubstantially the midpoint of said resistance to said anode, means lforgenerating saw-toothed sweep voltages, and transformer means forconnecting said generating means to said deilecting plates.

10. A cathode ray device comprising means for producing a moving beam ofelectrons, for accelerating said beam, means for producing deflection ofsaid beam comprising a pair o! electrostatic deiiecting plates, a highimpedance unit connected between said plates, meansv for connectingsubstantially the midpoint of said high impedance unit to generatingdefiecting voltages, and transformer said deecting plates.

`11. In a sweep circuit, a condenser, means comprising a source ofpotential for charging said condenser substantially linearly with re-vspect to time, means comprising an electron dis- 'charge device forperiodically discharging said` condenser, means for amplifying -the waveproduced by the charging and discharging of said condenser, and atransformer the primary wind- WILLIAM A. TOLSON.

an anode said anode, means for

